The commands in the Optopus package have to initialised by setting
the Optopus context with the MIDAS command SET/CONTEXT OPTOPUS.
All commands in this package have the qualifier OPTOPUS. Since
the majority of them need quite a number of input parameters, and where
their correct order and meaning is not always easy to remember, there
are are two ways to enter command parameters.
Besides the usual way of writing for each command:

command/qualifier p1 p2 p3 ...

it is also possible to define them in an explicit form:

SET/OPTOPUS param=value [param=value],

where param is the parameter name and value is the assigned
value. Every parameter set in this ways can be defaulted on the command
lines. Only the input and output filenames are required unless the general
default names are used (see documentation of the individual commands).
However, before executing a command it is recommended to check the session
parameters by listing them with the command SHOW/OPTOPUS. This will
produce an output table like in Table H.1. For a
complete overview see Section H.3.2.

Table H.1:
Parameters listed by SHOW/OPTOPUS

Input file:

mytab1.tbl

Output file:

mytab2.tbl

Plate label:

SA94

Plate center:

R.A.: 02h 43m 30.000s DEC.: -00d 15' 50.00"

Equinoxes:

Old : 1950.00000 New: 1991.76776

Date:

Year: 1991.00000 Month: 10. Day: 9. Epoch: 1991.76776

Exposure time:

120.0m

Wavelength range:

from: 4000. Ångstrom to: 8000. Ångstrom

Optimal sid. time slot:

from: 1h 0m to: 3h 0m

Optimal sid. time:

0.00h

ACFLAG:

N

PFLAG:

Y

ASTFLAG:

Y

EWFLAG:

N

The assigned values are maintained until the user gives the MIDAS
command CLEAR/CONTEXT or decides to leave the MIDAS session.
However, is is possible to save them with the command SAVE/OPTOPUS table, where table is the name of any table chosen
by the user. SAVE/OPTOPUS saves the relevant session parameters
by copying them to descriptors of table. It is advisable to use
this command, not only when you want to interrupt a session and restart
it later, but again during the session to protect yourself
against system crashes or accidental logouts of MIDAS. When
re-entering Optopus context, all parameters are re-initialised to the
default values but they can be re-set to the values of a previously
saved session with RESTORE/OPTOPUS table, where table is
of course the name of the table that contains the saved setting.

Since almost all commands in the package work, both in input and
in output, on MIDAS tables, another important task of the user at the
start of an Optopus session will be to create a MIDAS table from the
ASCII file where the data about the objects to be observed are being
kept. The newly created table will have to contain, amongst others,
an :IDENT and a :TYPE column, where :TYPE contains
``B'' or ``S'', respectively for ``big'' and ``small'' guidestars, and
``O'' for scientific object. As the format of this table is fixed and
crucial for all the following operations, there is a dedicated command
for this purpose:

A copy of this format file will be put in the working directis available in the file:

$MIDASHOME/$MIDVERS/stdred/optopus/incl/opto.fmt (UNIX)

MID_DISK:[MIDASHOME.MIDVERS.STDRED.OPTOPUS.INCL]OPTO.FMT (VAX/VMS)

so that it can be copied to the user's working directory and
subsequently modified according to the positions and field widths in
his/her ASCII file. You can copy the format file into your working
directory with the CREATE/OPTOPUS command itself. To do so
give the third parameter fmt_file in the command the value
copy. However, a copy will not be made if a file with the name
opto.fmt is already present.

In case the targets are already stored in a MIDAS table the user
should check if the table columns have the correct labels. If
required, modifications in the table can be made by using one or more
commands for table manipulation.

The equinox of the data has to be stored in the descriptor TABEQUI of the MIDAS table. It is important to verify whether the
equatorial coordinates have been precessed or not. In fact, next step
in this ``building-up'' of the Optopus session is the command:

PRECESS/OPTOPUS [inp_tab] [new_equinox],

which corrects the right ascension and declination for precession to
the date of the observation (this is the default, which can be changed
by defining the parameter NEWEQ), and updates the value of the
double precision descriptor TABEQUI. To limit the number of
files created in an Optopus session, this command will not to create a
new table, but will add two new columns :RA and :DEC in
the table created by CREATE/OPTOPUS. The old columns :RA
and :DEC are renamed to :OLDRA and :OLDDEC,
respectively. Note, that in this table the equatorial coordinates are
in decimal format.